1. Field of the Invention
The present invention relates to a scroll compressor and a vacuum preventing device of the scroll compressor, and more particularly, to a scroll compressor and a vacuum preventing device of the scroll compressor that are capable of preventing a compressor from being vacuumized by flowing back a gas at the side of a discharge pressure toward the side of a suction pressure in occurrence of an abnormal operation such as a pump-down or an expansion valve clogging.
2. Description of the Background Art
In general, a compressor, changing a mechanical energy to a latent energy of a compressive fluid, is divided into a reciprocating type, a scroll type, a centrifugal type and a vane type.
Among them, the scroll type compressor has a structure of sucking, compressing and discharging gas by using a rotor like the centrifugal type compressor or the vane type compressor, unlike the reciprocating type compressor which uses a linear reciprocal movement of a piston.
FIG. 1 is a vertical-sectional view showing inside of a conventional scroll compressor.
As illustrated, the conventional scroll compressor includes a case 1 having a gas suction tube (SP) and a gas discharge tube (DP), a main frame 2 and a sub-frame (not shown) installed, respectively, at both upper and lower sides of the inner circumferential surface of the case 1, a rotational shaft 4 coupled at a central portion of a drive motor 3 so as to transmit a rotational force of the drive motor 3, an orbiting scroll 5 installed eccentrically rotatable at an upper portion of the rotational shaft 4 and having an involute curve shaped wrap 5a at an upper portion thereof, and a fixed scroll 6 having an involute curve shaped wrap 6a so as to form a plurality of compression spaces (P) by being coupled with the orbiting scroll 5.
The case 1 is internally divided into a suction pressure zone (S1) and a discharge pressure zone (S2) by means of a high low pressure separation plate 7, and a middle pressure zone (S3) is formed communicating with the compression space (P).
A gas suction hole 6b and a gas discharge hole 6c are formed at the side and at the central portion of the fixed scroll 6, and a non-return valve 8 is installed at an upper surface of the fixed scroll 6 to prevent discharged gas from flowing backward.
The main frame 2 and the sub-frame are fixed at the inner circumferential surface of the case 1 by a typical fixing method such as welding, and the fixed scroll 6 is fixed at the lower surface of the high and low pressure separation plate 7 by means of a typical fixing unit such as a bolt.
In case of a pump down or an expansion valve clogging, the suction pressure zone (S1) of the compressor is in a high vacuum state, and at this time, a part of the compressor can be damaged. In order to prevent such a problem, a vacuum preventing device 20 is provided in the conventional art.
FIG. 2 is a vertical-sectional view showing an operation of the vacuum preventing device when the conventional scroll compressor is normally operated, FIG. 3 is a vertical-sectional view showing an operation of the vacuum preventing device when the conventional scroll compressor is not normally operated, and FIG. 4 is a sectional view taken along line A—A of FIG. 2.
With reference to FIGS. 2 and 3, The vacuum preventing device 20 is constructed such that a chamber 10 is formed at one side of the fixed scroll 6 and a discharge pressure hole 11 is formed at an upper surface of the chamber 10, communicating with the discharge pressure zone (S2).
A middle pressure hole 12 is formed at a lower surface of the chamber 10, communicating with the middle pressure zone (S3). A plug 14 having a suction pressure hole 13 is fixed by a fixing pin 15 at the side of an opening portion of the chamber 10. The suction pressure hole 13 communicates with the discharge pressure hole 11.
An open and shut member 17 is movably installed inside the chamber 10 to selectively communicate the discharge pressure hole 11 and the suction pressure hole 13.
A spring 16 is installed at the side of the opening portion of the chamber 10 to limit movement of the open and shut member 17 and provide an elastic force to the open and shut member 17.
The operation of the conventional scroll compressor constructed as described above will now be explained.
First, when power is applied to the drive motor 3, the drive motor 3 rotates the rotational shaft 4, and at this time, the orbiting scroll 5 coupled to the rotational shaft 4 is orbited as long as the eccentric distance.
At this time, the plurality of compression spaces (P) formed between the wrap 5a of the orbiting scroll 5 and the wrap 6a of the fixed scroll 6 are reduced in their volume as the orbiting scroll 5 is gradually moved toward the center of the fixed scroll 6 according to its continuous orbiting movement.
Owing to the continuous volume reduction of the compression spaces (P), the gas at the suction pressure zone (S2) is sucked into the compression spaces (P) through the suction hole 6b, and the sucked gas is discharged to the discharge pressure zone (S2) through the discharge hole 6c. 
When the compressor is normally operated, since the middle pressure (the pressure at the middle pressure zone) is stronger than the elastic force of the spring 16, the open and shut member 17 overcomes the elastic force of the spring 16 and close (seal) the discharge pressure hole 11. Conversely, if the compressor is not properly operated, since the middle pressure is weaker than the elastic force of the spring 16, the open and shut member 17 submits to the elastic force of the spring and opens the discharge pressure hole 11. At this time, the discharge pressure hole 11 communicates with the suction pressure hole 13.
As the discharge pressure hole 11 and the suction pressure hole 13 communicate with each other, the gas at the discharge pressure zone (S2) flows backward to the suction pressure zone (S1) through the discharge pressure hole 11 and the suction pressure hole 13, so that the vacuum of the compressor is released.
In the conventional scroll compressor, as shown in FIG. 4, a fine clearance (t) is formed between the inner-wall of the chamber 10 and the outer circumferential surface of the open and shut member 17 (that is, a gap formed between an upper surface of the inner wall of the chamber and an upper surface of the open and shut member), in order to induce a smooth sliding movement of the open and shut member 17.
Usually, the clearance (t) is formed with such a minimum size as to allow the open and shut member 17 to slidably move the chamber 10, and so fine as not to allow a gas to be leaked through the discharge pressure hole 11 when the open and shut member 17 closes the discharge pressure hole 11.
The finer the clearance (t) is, the more effectively the gas is blocked but the open and shut member 17 is not smoothly operated. Meanwhile, the greater the clearance (t) is, the more the gas is leaked but the open and shut member 17 is smoothly operated. Thus, in consideration of the open and shut member 17, the clearance (t) is designed and formed within a tolerance limit range.
However, in the conventional art, when the compressor is normally operated, the open and shut member 17 is downwardly pressurized by the gas pressure of the discharge pressure zone (S2), and at this time, the lower surface of the open and shut member 17 is tightly attached to the lower surface of the inner wall of the chamber 10 and at the same time the upper surface of the open and shut member 17 is isolated from the upper surface of the inner wall as much. That is, the clearance (t) is increased beyond the tolerance limit range.
With the increased clearance, the gas at the discharge pressure zone is partially leaked to the suction pressure zone through the clearance, resulting in degradation of the compression efficiency of the compressor.
In addition, in the conventional art, a precision is required so high as to enough satisfy those problems in designing and forming the clearance, fabrication cost is high and a productivity is degraded.